METHOD FOR FORMING A CONTAINER

Abstract

Method for forming a container, includes the steps of: positioning a first preform made of plastic material in a forming chamber of the mould; counter-shaping the first preform to the mould obtaining the first container; the step of counter-shaping the first preform includes the step of performing a blowing of the first preform placed inside the forming chamber; at least a portion of a surface of the mould which delimits the forming chamber being shaped to obtain an opacification of at least a portion of the first container; cooling the first container by introducing a gaseous stream into the container for fixing the opacification on the first container; removing the first container from the mould; and keeping the mould at a higher temperature than room temperature at least from the step of performing the blowing to that of removing the first container.

Claims

1. A method for forming a container, comprising the steps of: positioning a first preform (10) made of plastic material in a forming chamber (20) of the mould (2); counter-shaping the first preform (10) to the forming chamber (20) obtaining the first container (100); the step of counter-shaping the first preform (10) comprises the step of performing a blowing the first preform (10) placed inside the forming chamber (20); at least a portion of a surface of the mould (2) which delimits the forming chamber (20) being shaped to obtain an opacification of at least a portion of the first container (100); characterised by: cooling said first container (100) by introducing a gaseous stream into the container (100) for fixing the opacification on the first container (100); removing said first container (100) from the mould (2); keeping said mould (2) at a higher temperature than room temperature at least from the step of performing said blowing of the first preform (10) to that of removing said first container (100).

2. The method according to claim 1, characterised in that said step of keeping said mould (2) at a higher temperature than room temperature comprises the step of keeping the maximum temperature time trend of said mould (2) within a range of about 30 C. at least from the step of performing said blowing of the first preform (10) to that of removing said first container (100).

3. The method according to claim 1, characterised in that said step of keeping said mould (2) at a higher temperature than room temperature comprises the step of keeping said mould (2) at a maximum temperature higher than 60 C. at least from the step of performing said blowing of the first preform (10) to that of removing said first container (100).

4. The method according to claim 1, characterised in that said step of keeping said mould (2) at a higher temperature than room temperature comprises the step of keeping the maximum temperature of said mould (2) comprised between 60 C. and 180 C. at least from the step of performing said blowing of the first preform (10) to that of removing said first container (100).

5. The method according to claim 1, characterised in that the step of keeping said mould (2) at a higher temperature than room temperature takes place by means of a heating element (3) external to a forming chamber (20) in which the first preform (10) is placed.

6. The method according to claim 1, characterised in that the step of counter-shaping the first preform (10) to the mould (2) comprises the step of stretching the first preform (10) by means of a stretching rod (11) which projects internally to the first preform (10); the step of introducing a gaseous stream into the container (100) takes place by dispensing the gaseous stream through at least one hole placed on the stretching rod (11); the step of performing the blowing of the first preform (10) comprises the step of introducing into the first preform (10) a fluid through at least one nozzle external to the stretching rod (11).

7. The method according to claim 1, characterised by: introducing a second preform after the step of removing the first container (100); performing the blowing of the second preform obtaining a second container; cooling a wall of said second container by introducing a gaseous stream into the second container for fixing the opacification obtained onto the container; removing said second container from the mould (2); keeping said mould (2) at a higher temperature than room temperature comprises the step of keeping said mould (2) at a maximum temperature higher than 60 C. at least from the step of introducing the first preform (10) to the step of removing the second container.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Further characteristics and advantages of the present invention will become more apparent from the approximate and thus non-limiting description of a method for forming a container, as illustrated in the appended FIG. 1, which represents a schematic view of the apparatus for implementing the method.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0007] The subject matter of the present invention is a method for forming a container 100 (this container has at least one opaque part). The method comprises the step of positioning a first preform 10 in a forming chamber 20 of the mould 2. During the present discussion for simplicity purposes reference is made to one forming chamber 20, but there may be several forming chambers. Appropriately, in that case, the method would be identical and simultaneous in each of the forming chambers 20. Appropriately, the first preform 10 is made of plastic material, for example PET. The mould 2 may appropriately comprise several half-moulds that can be moved towards/away from one another. When they are moved towards one another, they thus define the forming chamber 20; when they are moved away from one another they enable the removal of the container. For example, the half-moulds could comprise two lateral portions that can be moved towards/away from one another and possibly a lower bottom.

[0008] Appropriately, the method envisages the mould 2 being hot. The method also comprises the step of heating the mould 2 at least at the beginning of the forming process (before shaping the initial preform). Then, the mould 2 is advantageously kept at such temperature and various preforms are inserted in succession, removing the related containers.

[0009] The method comprises the step of counter-shaping the first preform 10 to the forming chamber 20 obtaining the first container 100; the step of counter-shaping the first preform 10 comprises the step of performing a blowing of the first preform 10 inside the forming chamber 20. In this way the container 100 is obtained (schematically illustrated with a broken line in FIG. 1). At least one portion of a surface of the mould 2 that delimits the forming chamber 20 is shaped to obtain opacification of at least one portion of the first container 100. For example, this portion of surface could have discontinuities, e.g. it may be knurled or wrinkled or have a pattern of raised areas. In this way the surface of the first container 100, coming into contact with these discontinuities while still hot, follows these discontinuities and becomes opaque.

[0010] The step of performing a blowing of the first preform 10 advantageously but not necessarily comprises the step of introducing into the first preform 10 a fluid for a period of at least 2 seconds.

[0011] The step of counter-shaping the first preform 10 to the mould 2 may comprise the step of stretching the first preform 10 by means of a stretching rod 11 which projects internally to the first preform 10. The stretching rod 11 exerts a stretching action internal to the first preform 10 which facilitates blowing in the operation of correctly shaping the first preform 10.

[0012] The method comprises the step of cooling the first container 100 by introducing a gaseous stream into the container 100. In this way, the opacification is fixed onto the first container. The opacification thus remains stable and permanent. In fact, as the first container 100 cools, the opacification is consolidated together with the rest of the first container 100. Alternatively, if the first container 100 were removed from the mould 2 still hot (and thus malleable) without appropriate cooling it could lose the opacification or even collapse.

[0013] The step of cooling the first container 100 by introducing a gaseous stream into the container 100 takes place after the blowing step has been performed. Appropriately, the gaseous stream is introduced at a temperature comprised between 20 C. and 50 C.

[0014] The step of introducing a gaseous stream into the container 100 preferably takes place by dispensing the gaseous stream through at least one hole placed on the stretching rod 11. The step of performing a blowing of the first preform 10 comprises the step of introducing into the first preform 10 a fluid through at least one nozzle external to the stretching rod 11 (e.g. at least one nozzle external to the first preform 10 or which projects internally to the first preform 10). Therefore, the blowing fluid and gaseous stream can be introduced into the first preform/first container by the same conduit or separate conduits.

[0015] Appropriately, the step of introducing a gaseous stream into the container 100 for cooling it takes place by introducing a gaseous stream for a period greater than 2 seconds (however this duration varies according to various parameters, e.g. the shape to be obtained and the material). Appropriately, this gaseous stream is recirculated inside the forming chamber 20.

[0016] Possibly, between the dispensing of the blowing fluid and the dispensing of the gaseous stream there may be a time period in which nothing is dispensed into the preform/container. Appropriately, once one step is finished the other begins straight away.

[0017] Appropriately, the blowing fluid is air. Appropriately, the gaseous cooling stream is air. Therefore, the fluid and the gaseous stream may be the same fluid.

[0018] The method envisages removing the first container 100 from the mould 2. Appropriately, the step of removing the first container 100 from the mould 2 takes place with the first container 100 at a maximum temperature of less than 40 C. In an alternative solution, the step of removing the first container 100 from the mould 2 takes place with the first container 100 at a temperature comprised between 40 and 80 C., but in that case the first container 100 is placed in an auxiliary cooling chamber to complete the cooling process.

[0019] The method envisages keeping the mould at a higher temperature than room temperature at least from the step of performing the blowing to that of removing the first container 100 from the mould 2.

[0020] The step of keeping the mould 2 a higher temperature than room temperature takes place by means of a heating element 3 external to a forming chamber 20 in which the first preform 10 is placed.

[0021] For example, the heating element 3 may be an electrical resistor or a heating fluid that circulates in one or more conduits, etc. Appropriately, this heating fluid transits, at least for a section, inside the thickness of the walls of the mould 2.

[0022] The method does not envisage the use of elements dedicated to the cooling of the mould 2. In particular, no cooling element intervenes directly on the mould 2. The mould 2 is heated to keep it at that temperature considering normal dissipations and the fact that introducing a gaseous cooling fluid into the preforms would eventually cool it down. The cooling of the mould 2 is in general to be avoided. The first preform 10 is introduced into the mould 2 at high temperature (e.g. at a temperature greater than 80 C.) and removed with the mould at high temperature (e.g. at a temperature greater than 80 C.).

[0023] In particular, the step of keeping said mould 2 at higher temperature than room temperature comprises the step of keeping the maximum temperature time trend of said mould 2 within a range of about 30 C. (at least from the step of performing said blowing to that of removing said first container 100). In a particular non-limiting embodiment, for example, it could fluctuate between 60 and 150 C. The temperature of the mould 2 is quite uniform, but the maximum temperature is the maximum temperature detectable moment by moment in/on walls of the mould 2.

[0024] For example, the step of keeping the mould 2 at a higher temperature than room temperature comprises the step of keeping said mould 2 at a maximum temperature greater than 60 C. (preferably greater than 100 C.) at least from the step of performing said blowing to that of removing said first container 100.

[0025] Even more precisely, the step of keeping said mould 2 at a higher temperature than room temperature comprises the step of keeping the maximum temperature of said mould 2 comprised between 60 C. and 180 C. at least from the step of performing said blowing to that of removing said first container 100.

[0026] The method also comprises the steps of: [0027] introducing a second preform after the step of removing the first container 100; [0028] performing a blowing of the second preform obtaining a second container; in the appended FIGURE the second preform and the second container may hypothetically be identical to the first preform 10 and the first container 100; [0029] cooling a wall of said second container by introducing a gaseous stream into the second container for fixing the opacification obtained onto the second container; [0030] removing said second container from the mould 2; [0031] keeping said mould 2 at a temperature higher than room temperature. The latter step of keeping said mould 2 at a higher temperature than room temperature comprises the step of keeping said mould 2 at a maximum temperature higher than 80 C. at least from the step of introducing the first preform 10 to the step of removing the second container. The numeral adjective first in the present discussion is only used to distinguish the preforms or containers from one another.

[0032] The present invention achieves important advantages.

[0033] Above all, it enables the cycle times to be reduced. This enables to speed up and increase production. In fact, the external mould 2 is not continuously heated to then be cooled in order to cool the preform.

[0034] Furthermore, the present invention enables the overall construction complexity of the machine to be reduced and thus the costs to be reduced. The invention as it is conceived is susceptible to numerous modifications and variants, all falling within the scope of the inventive concept characterised thereby. Further, all the details can be replaced with other technically equivalent elements. In practice, all the materials used, as well as the dimensions, can be any whatsoever, according to need.